1. Field of the Invention
The invention relates in general to a fluorescent material, and particularly a light emitting device using the fluorescent material.
2. Description of the Related Art
In recent years, light emitting devices utilizing semiconductors for emitting lights have been intensively used. In particular, light emitting diodes (LED) have been developed successfully. Compared to conventional light emitting equipments, such as cold cathode fluorescent lamps and incandescent lamps, light emitting devices utilizing light emitting diodes have advantages of high emitting efficiency, small volumes, low power consumption, and low cost. Therefore, such light emitting devices are used in various light sources. Semiconductor light emitting devices comprise semiconductor light emitting elements and fluorescent materials. Fluorescent materials can absorb and convert lights emitted from semiconductor light emitting elements. Lights emitted directly from semiconductor light emitting elements and lights converted by fluorescent materials can be mixed for use. Such light emitting devices can be used in various areas, such as fluorescent lights, car lighting, display devices, and liquid crystal backlights.
Current white LED light emitting devices are developed according to anaglyphic principle. Fluorescent materials absorb a blue light emitted from semiconductor light emitting elements and convert it into a yellow light. When the blue light and the yellow light enter human eyes simultaneously, a white light is observed by the human. For example, the above-mentioned effect can be achieved via a semiconductor of InGaN and a yellow fluorescent material having a general formula of (Y,Gd)3(Al,Ga)5O12:Ce.
Further, a white light can be generated by utilizing a combination of a light emitting element which emits ultraviolet lights and a fluorescent material which emits g RGB (red, green, and blue) lights. Furthermore, when a light emitting element emits an ultraviolet light, the ultraviolet light is converted by a fluorescent material to emit a blue light, and then another fluorescent material is excited by the blue light to emit a yellow light, as such, a white light is generated by mixing the blue light and the yellow light.
However, light emitting devices have been used in more and more areas, and the luminous brightness of the commercially yellow fluorescent material (Y,Gd)3(Al,Ga)5O12:Ce series is evidently insufficient, therefore, the industrial needs are not satisfied. In addition, when luminous brightness is increased, luminescent chromaticity shift easily occurs. Therefore, developing a fluorescent material which satisfies the needs for various applications of light emitting devices as well as increases luminance has become one of the most important goals.